1. Field of the Disclosure
This disclosure resides in the field of wound healing compositions and use thereof. Particularly, this disclosure relates to compositions of heat shock proteins (hsp), specifically, the hsp90-alpha (hsp90α) and its derivatives and the topical application of these compositions to human skin wounds to expedite the wound healing process by promoting both epidermal and dermal cell migration.
2. Description of the Related Art
Thirteen percent of Americans are currently 65 years old or older. From 1995 to 2050, this age group is expected to more than double in size. According to the Wound Healing Society, 15% of them suffer from chronic, hard-to-heal wounds. Among the two million people diagnosed yearly with pressure ulcers, 900,000 have non-healing lower extremity ulcers. It is estimated that 18% of patients with diabetes over the age of 65 will have chronic, non-healing foot ulcers. Moreover, 50,000 lower extremity amputations are performed each year due to infected lower leg chronic wounds. The quality of life due to morbidity of non-healing leg ulcers is significantly compromised because of wound odor, infection, and pain. In addition, these issues also lead to social isolation and diminished self-image in patients with chronic skin wounds. Financially, the cost for managing delayed wound healing in the US elderly is estimated at $9 billion per year.
Tremendous effort has been made to develop recombinant growth factors and organotypic skin equivalents for therapy for non-healing wounds. Purchio et al. teaches in U.S. Pat. No. 5,599,788, a method for accelerating skin wound healing with recombinant transforming growth factor β-induced H3 protein by promoting adhesion of human dermal fibroblasts. It was shown that H3 protein promoted adhesion of human dermal fibroblasts to tissue culture plastic.
Akella et al. discloses in U.S. Pat. No. 7,081,240, the use of a protein mixture for treating wounds, wherein the mixture is isolated from bone or produced from recombinant proteins such as bone morphogenetic proteins, transforming growth factors and fibroblast growth factors. However, the overall clinical outcomes of growth factor therapy have been disappointing and few growth factors have ultimately received FDA approval.
Kiss discusses the use of non-growth factor proteins for use in wound healing comprised of human alpha1-antitrypsin, human placental alkaline phosphatase, human transferring and α1-acid glycoprotein. However, this method requires the complicated sequential application of several agents that act at different steps, and also may require adjustment of the compositions according to each treatment.
In chronic wounds, keratinocyte migration is blocked and the wounds remain open, causing patient morbidity and even fatality. During human skin wound healing, a critical rate-limiting step is the initiation of the resident epidermal and dermal cells at the wound edge to migrate into the wound bed. Human keratinocytes (HKCs) laterally migrate across the wound bed from the cut edge to eventually close the wound, the process known as re-epithelialization. The dermal cells, including dermal fibroblasts (DFs) and dermal microvascular endothelial cells (HDMECs), start to move into the wound following the HKC migration, where these cells deposit matrix proteins, contract and remodel the newly closed wound and build new blood vessels. HKC migration is largely driven by TGFα in human serum and is not affected by high concentrations of TGFβ family cytokines co-present in human serum.
In contrast, the presence of TGFβ blocks the dermal cell migration even in the presence of their growth factors, such as PDGF-BB and VEGF. Therefore, while it is understandable why HKC migration jumpstarts ahead of DF and HDMEC migration during wound healing, it has remained as a puzzle how DFs and HDMECs move into the wound bed in the presence of abundant TGFβ.
The heat shock protein (hsp) families include chaperon proteins that are either constitutively expressed, such as the hsp90 family, or stress-induced expression, such as the hsp70 and hsp27 families. Historically, their function is restricted to intracellular proteins, where they interact with and facilitate proper folding and intracellular trafficking of the target proteins to maintain cellular homeostasis and to promote cell survival.
Recently, hsp proteins were found to be actively secreted by cells and carry out important extracellular functions, including stimulation of immunological cytokine production, activation of antigen presenting cells (APCs) and anti-cancer functions. Hypoxia causes hsp90α secretion in both epidermal and dermal cells. The secreted hsp90α in turn promotes migration of these cells. Since hsp proteins lack any signal sequences at the amino terminus, these proteins cannot be secreted via the classical endoplasmic reticulum/Golgi transport pathway. Instead, these proteins are secreted to outside of the cells by a discrete population of nano-vesicles (30-90 nm in diameter), called exosomes. Therefore, the exosome secretion constitutes a potential mode of intercellular communication and opens up new therapeutic and diagnostic strategies. TGFα “pushes” hsp90α out of the human keratinocytes via the exosome pathway, which in turn promotes migration of both the epidermal and dermal cells through the cell surface receptor CD91/LRP-1 (“LRP” meaning LDL receptor-related protein-1).